Non-corrosive hydraulic fluid



United States Patent 3,324,036 NON-CORROSWE HYDRAULIC FLUID Richard W. Shilfier, Briarclitf Manor, N.Y., assignor t0 gnizlm Carbide Corporation, a corporation of New or r No Drawing. Filed May 11, 1965, Ser. No. 454,958 3 Claims. (Cl. 25275) This application is a continuation-in-part of application Ser. No. 117,503, filed June 16, 1961, which was a continuation of application Ser. No. 633,178, filed Jan. 9, 1957, both of which are now abandoned.

This invention relates to alkaline-inhibited hydraulic liquid compositions, which are non-corrosive to nonferrous metals, and which are free and remain free of precipitates which tend to clog small orifices or otherwise interfere with the operation of hydraulic systems, and to methods for preventing corrosion of non-ferrous metals by alkaline-inhibited hydraulic fluids. More particularly, this invention is directed to alkaline-inhibited hydraulic liquid compositions which contain alcohols, alcohol ethers, or both, and organic orthosilicates having not more than 48 carbon atoms to the molecule. By the term organic orthosilicates, as used herein, is meant organosilicon compounds characterized by only alkoxy or only aryloxy groups attached to a single silicon atom or to groups of silicon atoms interconnected by silicon to oxygen to silicon bonds, i.e.,

Ethyl silicate has been used heretofore in heat transfer liquids which are mainly aqueous solutions of alcohols to inhibit corrosion of cooling system metals. The lowest concentration of ethyl silicate which was found to be effective in inhibiting corrosion in such heat transfer liquids was 0.01 percent of the silicate based on the weight of non-aqueous alcohol present.

Alkaline inhibitors have been used in hydraulic fluids for the purpose of preventing corrosion of ferrous metals of hydraulic systems. Such alkaline-inhibited hydraulic fluids, however, can be corrosive toward such non-ferrous metals as aluminum, brass, copper as well as cast iron.

We have found that akaline-inhibited hydraulic liquids containing (a) at least one compound from the class of alcohols and their ethers and (b) not-more than 0.009 weight percent, preferably not more than 0.005 weight percent, and as low as 0.0001 weight percent, of an organic orthosilicate having not more than 48 carbon atoms to the molecule (percentage based on the weight of the alcohol, the ether, or the mixture of the two), adequately inhibit corrosion of non-ferrous metals, such as, aluminum, copper and brass without forming heavy precipitates of the nature which interfere with the operation of hydraulic systems. In fact, it has been observed that concentrations of organic orthosilicates in hydraulic fluids which are 0.01 percent and above based on the weight of the alcohol, the ether, or both, tend to promote heavy precipitates which obviously can interfere with the operation of a hydraulic system by clogging small orifices and obstructing the motion of moving parts or the movement of fluid in the hydraulic lines. Although not wishing to be bound by any particular theory, it is believed that even small amounts of water inevitably present in any hydraulic system hydrolyze organic orthosilicates, which in amounts of 0.01 weight percent and above form heavy precipitates. Water can enter a hydraulic system by leakage, condensation from the atmosphere and/or by absorption of moisture from the atmosphere. Brake fluids after a few years use have been found to contain up to 5 percent by weight of water.

Lubricant 15 to 35 Diluent 65 to Antioxidant 0 to 2 Alkaline inhibitor 0.1 to 2 Organic orthosilicate 0.0001 to 0.009

The lubricant portion contains one or more polyhydric alcohol or polyhydric alcohol ether including polyethers, or a mixture of polyhydric alcohols and ethers, all preferably having average molecular weights of at least about 300 as a minimum. The lubricant may also contain, as modifiers, esters and polyesters of polyhydric alcohols, reaction products of alkylene oxides and polyfunctional aimnes, e.g., polyalkylene polyamines, ethanolamines and the like, castor oil, blown castor oil, i.e., castor oil which is polymerized by air oxidation, bodied castor oil, i.e., castor oil which is polymerized by heat alone, acetylated castor oil, glycol modified castor oil and the like or mixtures thereof. The diluent portion acts as a solvent permitting adjustments to the composition viscosity, as desired and can comprise one or more monohydric alcohols or dihydric alcohol monoethers or mixtures thereof and can contain from 0 to 50 weight percent dihydric alcohols all of which have average molecular weights below about 300. The antioxidants and alkaline inhibitors are known in the art.

Any method desired can be used in preparing our hydraulic liquid compositions. The components can be added together or one at a time in any desired sequence. However, it is preferable to add the antioxidant and alkaline inhibitor as a solution in the alcohol component. It is also preferable to warm this solution during its preparation in order to facilitate dissolution. All components are mixed until a single phase composition is obtained.

Typical organic orthosilicates include tetraalkylorthosilicates, such as, tetramethylorthosilicate, tetraethylorthosilicate, tetrapropylorthosilicate, tetrabutylorthosilicate, tetraamylorthosilicate, tetra 2 ethylhexylorthosilicate, tetradecylorthosilicate, tetraarylorthosilicate, such as, tetraphenylorthosilicate, polysilicates such as hexa(2-cthylbutoxy)disiloxane, the polysilicate known as ethyl silicate 40, and the like. The polysilicate known as ethyl silicate 40 is a mixture of series of organo-silicon compounds composed of two or more silicon atoms interconnected by ether oxygen and having ethoxy groups attached to the remaining valences of said silicon atoms, the lowest member of the series being hexaethoxydisiloxane. Such mixtures are identified by their silicon dioxide content, ethyl silicate 40 containing 40 weight percent silicon dioxide. The preparation of such polysilicates are known in the 'art. An advantageous method for preparing these polysilicates is by the reaction of silicon-tetrachloride and aqueous ethanol, although other methods can be used. Of the organic silicates, tetraethylorthosilicate is preferred.

Representative of polyhydric alcohols which can be used in our liquid compositions are the alkylene glycols, e.g., ethylene glycol, propylene glycol, the butanediols, the pentanediols, the hex'anediols and the like, the polyoxyalkylene glycols such as polyoxyethylene glycols, polyoxybutylene glycols and the like, mixed polyoxyalkylene glycols, e.g., polyoxyethylene-polyoxypropylene glycols, and polyoxyalkylene triols. Representative of polyhydric alcohol ethers are the alkyl and aryl monoethers, diethers and triethers of polyhydric alcohols such as those specified above. Example of polyhydric alcohol ethers are ethylene glycol monomethyl ether, dipropylene glycol monoethyl ether, polyoxyethylene glycol monophenyl ether and the like, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, polyoxypropylene glycol dibutyl ether and the like.

Typical antioxidants include phenolic compounds, such as, 2,2-di(4-hydroxyphenyl)propane and polymerized trimethyldihydroxyquinoline and the like, amines, such as, phenyl alphanaphthylamine and phenyl beta-naphthylamine, and the like, as well as hindered phenols and the like.

Alkaline inhibitors are well known in the art. For instance, useful alkaline inhibitors include sodium borate, potassium borate, sodium hydroxide, potassium hydroxide, amines and amine salts, such as monoor dibutyl ammonium borates, phosphates and dilinoleates, and the like. Preferred classes of alkaline inhibitors include the alkali metal borates such as lithium borate, sodium borate, potassium borate, and the like; and the amines and amine salts such as alkanolamines such as triethanolamine, triisopropanolamine, and the like, alkylamines such as butylamine, dibutylamine, tributylamine, pentylamine, dipentylamine, and the like, alkylammonium borates such as butylammonium borate, dibutylammonium borate, pentylammonium borate, and the like, alkylammonium phosphates such as butylammonium phosphate, hexylammonium phosphate, and the like, alkylammonium salts of long chain hydrocarbon carboxylic acid such as butylammonium dilinoleate, butylammonium diricinoleate, and the like. Although the amines and amine salts may not corrode aluminum they can corrode brass and copper. The addition of silicates minimizes or eliminates such corrosion.

The following examples are presented:

Example 1 A mixture containing the following materials was prepared. Parts by volume Polyoxyethylene-polyoxypropylene glycol monobutyl ether having a viscosity of about 2000 Saybolt Universal seconds at 25 C. 15.00 Polyoxyethylene-polyoxypropylene glycol monobutyl ether having a viscosity of about 260 Saybolt Universal seconds at 25 C. 17.50 Ethylene glycol monobutyl ether 33.75 Diethylene glycol monoethyl ether 25.49 Ethylene glycol 8.26

Example 2 To 100 parts by weight of the alkaline-inhibited mixture of fluid prepared in Example 1, 0.002 part by weight of tetraethylorthosilicate was added and dissolved. The hydraulic liquid composition thus made was prepared for corrosion testing by incorporating therein 5 parts by volume of water. Six strips, one each of the following (bolted together in the order listed) tin, steel, aluminum, cast iron, brass and copper, were immersed in the hydraulic liquid-water solution and the temperature of the solu tion was raised to 212 F. This temperature was maintained for 5 days. At the end of this period all of the 4- strips were clean and bright and there was not more than a trace of precipitation, if any, in the solution. The same test using the alkaline-inhibited mixture of Example 1, without added silicate, caused corrosion and discoloration of aluminum.

Example 3 testing, all of the strips were clean and bright and no precipitation was evident in the solution.

Example 4 Three hydraulic liquid compositions each containing parts by weight of the alkaline-inhibited mixture made in Example 1 and, respectively, 0.00125, 0.0025 and 0.005 part by weight of tetraethylorthosilicate were prepared. Similarly, two fluids were prepared from 100 parts by weight each of the alkaline-inhibited mixture made in Example 1 and, respectively, 0.01 and 0.02 parts by weight of tetraethylorthosilicate. To 100 parts by volume of each of the hydraulic liquids and the fluids, 3.5 parts by volume of water were added and mixed therewith. Each water mixture thus prepared was heated at F. for 24 hours and inspected. The fluids containing, respectively, 0.02 and 0.01 part by Weight of tetraethylorthosilicate formed heavy precipitates. The hydraulic liquid containing 0.005 part by weight of tetraethylorthosilicate was clear containing at most only a bare trace of flocculent material. The hydraulic liquids containing, respectively, 0.00125 and 0.0025 part by weight of tetra ethylorthosilicate were clear and free of any solid material.

Example 5 A mixture containing the following materials was prepared,

Parts by volume Polyoxyethylene-polyoxypropylene glycol monobutyl ether having a viscosity of about 260 Saybolt Universal seconds at 25 C 25 Diethylene glycol monoethyl ether 61 Polyoxypropylene glycol having an average molecular weight of about 5 Ethylene glycol 4 Reaction product of about equal parts by weight of castor oil and polyoxypropylene glycol (average molecular weight of about 150) A hydraulic liquid composition was prepared from 100 parts by weight of the alkaline-inhibited mixture or fluid prepared in Example 5 and 0.001 part by Weight of tetraethylorthosilicate. This hydraulic liquid was prepared for testing and tested as specified in Example 2 with tin, steel, aluminum, cast iron, brass and copper strips. After 5 days at a temperature of 212 F. the strips were withdrawn from the test solution and were found to be clean and bright, There was no precipitation evident in the test solution. Thi test was repeated employing the alkaline-inhibited mixture of Example 5 without an organic orthosilicate resulting in corrosion and discoloration of aluminum.

Example 7 A hydraulic liquid compositionwas prepared from 100 parts by weight of the alkaline-inhibited mixture or fluid made in Example 5 and 0.0015 part by weight of ethyl silicate 40. This hydraulic liquid was prepared for testing and was tested in accordance with the method specified in Example 2 with tin, steel, aluminum, cast iron, brass and copper strips. After 5 days at a temperature of 212 F. the strips were removed from the test solution and found to be clean and bright. There was no evidence of precipitation in the test solution.

What is claimed is:

1, An alkaline-inhibited hydraulic fluid consisting essentially of (a) a lubricant consisting essentially of at least one polyhydric alcohol or ether thereof having an average molecular weight of at least about 300, (b) a diluent consisting essentially of at least one monohydric alcohol or dihydric alcohol monoether, and up to about 50 weight percent of dihydric alcohol, having an average molecular weight below about 300, (c) an alkaline inhibitor selected from the group consisting of alkali metal hydroxides, alkali metal borates, alkanolamines, alkylamines, alkyl ammonium borates, alkylammonium phosphates, and alkylammonium salts of long chain hydrocarbon carboxylic acids, and (d) from 0.0001 to 0.005 weight percent, based on weight of said hydraulic fluid, of an organic orthosilicate selected from the group consisting of silicates having one silicon atom and silicates having a plurality of silicon atoms interconnected by silicon-to-oxygen-to-silicon bonds, the organic groups of said organic orthosilicate being selected from the group consisting of alkoxy and aryloxy attached to silicon, said organic orthosilicate having not more than 48 carbon atoms per molecule, wherein said lubricant is present in said hydraulic fluid in an amount within the range from about 15 to about weight percent, wherein said diluent is present in said hydraulic fluid in an amount within the range of from about to about 85 weight percent, and wherein said alkaline inhibitor is present in said hydraulic fluid in an amount within the range of from about 0.1 to about 2 weight percent, the percentages being based upon the weight of said lubricant plu said diluent,

2. The alkaline-inhibited hydraulic fluid of claim 1 wherein the organic orthosilicate is tetraethyl orthosilicate.

3. The alkaline-inhibited hydraulic fluid of claim 1 wherein the lubricant is polyoxyalkylene glycol monoalkyl ether, the diluent is alkylene glycol monoalkyl ether and alkylene glycol, the alkaline inhibitor is an alkali metal borate, and the organic orthosilicate is tetraethyl orthosilicate.

References Cited UNITED STATES PATENTS 2,349,338 5/1944 Clapsadle et al 252- LEON D. ROSDOL, Primary Examiner. R. D. LOVERING, Assistant Examiner. 

1. AN ALKALINE-INHIBITED HYDRAULIC FLUID CONSISTING ESSENTIALLY OF (A) A LUBRICANT CONSISTING ESSENTIALLY OF AT LEAST ONE POLYHYDRIC ALCOHOL OR ETHER THEREOF HAVING AN AVERAGE MOLECULAR WEIGHT OF AT LEAST ABOUT 300, (B) A DILUENT CONSISTING ESSENTIALLY OF AT LEAST ONE MONOHYDRIC ALCOHOL OR DIHYDRIC ALCOHOL MONOETHER, AND UP TO ABOUT 50 WEIGHT PERCENT OF DIHYDRIC ALCOHOL, HAVING AN AVERAGE MOLECULAR WEIGHT BELOW ABOUT 300, (C) AN ALKALINE INHIBITOR SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL HYDROXIDES, ALKALI METAL BORATES, ALKANOLAMINES, ALKYLAMINES, ALKYL AMMONIUM BORATES, ALKYLAMMONIUM PHOSPHATES, AND ALKYLAMMONIUM SALTS OF LONG CHAIN HYDROCARBON CARBOXYLIC ACIDS, AND (D) FROM 0.0001 TO 0.005 WEIGHT PERCENT, BASED ON WEIGHT OF SAID HYDRAULIC FLUID, OF AN ORGANIC ORTHOSILICATE SELECTED FROM THE GROUP CONSISTING OF SILICATES HAVING ONE SILICON ATOM AND SILICATES HAVING A PLURALITY OF SILICON ATOMS INTERCONNECTED BY SILICON-TO-OXYGEN-TO-SILICON BONDS, THE ORGANIC GROUPS OF SAID ORGANIC ORTHOSILICATE BEING SELECTED FROM THE GROUP CONSISTING OF ALKOXY AND ARYLOXY ATTACHED TO SILICON, SAID ORGANIC ORTHOSILICATE HAVING NOT MORE THAN 48 CARBON ATOMS PER MOLECULE, WHEREIN SAID LUBRICANT IS PRESENT IN SAID HYDRAULIC FLUID IN AN AMOUNT WITHIN THE RANGE FROM ABOUT 15 TO ABOUT 35 WEIGHT PERCENT, WHEREIN SAID DILUENT IS PRESENT IN SAID HYDRAULIC FLUID IN AN AMOUNT WITHIN THE RANGE OF FROM ABOUT 65 TO ABOUT 85 WEIGHT PERCENT, AND WHEREIN SAID ALKALINE INHIBITOR IS PRESENT IN SAID HYDRAULIC FLUID IN AN AMOUNT WITHIN THE RANGE OF FROM ABOUT 0.1 TO ABOUT 2 WEIGHT PERCENT, THE PERCENTAGES BEING BASED UPON THE WEIGHT OF SAID LUBRICANT PLUS SAID DILUENT. 